Method and apparatus for reducing inter-cell interference

ABSTRACT

A method is described for reducing interferences in a wireless network, by: identifying cells which experience more interference than others; identifying a group of PRBs that their transmissions are subjected to moire interference than other concurrent transmissions; identifying UEs associated with the group of PRBs, and determining whether the location of the UEs is at the cells&#39; edges; selecting a pair of UEs where one member is located at a first cell&#39;s edge and the other is located either (i) at a second cell, not included within a neighbors&#39; list of the first cell, or (ii) at the core or remote edge of a second cell. In case (i), the second cell is introduced to the first cell neighbors&#39; list, and in case (ii) the other UE is falsely defined as a UE located at the near second cell&#39;s edge. Then, ICIC procedure is invoked for that pair of UEs.

TECHNICAL FIELD

The invention relates to a system and a method for managing wirelessnetworks, and in particularly to management of interference in cellularmobile communication systems.

BACKGROUND

In current cellular mobile broadband systems the achievable data ratesare strongly dependent on the users' positions in the network.

Even though it is of great importance to deliver the same userexperience across the whole cellular network in order to meet the users'expectations, still, a considerable gap is observed between cell-edgeand cell-core performance due to inter-cell interference, which posesthe main limitation of state-of-the art mobile networks.

Long Term Evolution (“LTE”) is the 4th generation cellular mobile systemthat is being developed and specified in 3GPP as a successor of theUniversal Mobile Telecommunications System (“UMTS”) standard which wasadopted by third generation mobile cellular systems for networks basedon the GSM standard. LTE is specified as frequency reuse-1 systemdesigned to achieve maximum gain and efficient use of frequencyresources. On one hand, the optimal use of resources provides higher bitrates while on the other hand it generates Inter Cell Interference (ICI)issues associated with the reuse-1 type of deployment. In the absence ofany interference mitigation or coordination mechanism, ICI becomescritical in LTE, and as described above, especially on cell borders.Therefore, a number of schemes have been suggested for the mitigationsolution of ICI, and are typically classified as static and dynamic onthe basis of their type of interference coordination mechanisms.

One of these types is centralized ICIC (“cICIC”) which has the advantageof addressing interference issues that distributed ICIC (“dICIC”), whichis implemented at the eNodeB level, is incapable of handling.

The evolution of the physical layer of the cellular radio access hasreached nowadays a level where operation close to theoretical limits ofachievable spectral efficiency for a given signal tointerference-and-noise (SINR) ratio, becomes feasible. Thus, significantincreases in spectral efficiency can be achieved only by improving theSINR through minimization of the interference.

The 3GPP LTE Recommendation defines two types of interferenceminimization techniques. The first one being interference minimizationby interference reduction, whereas the second one is interferenceminimization by inter cell interference coordination (ICIC). The 3GPPstandard handles the two types of interference minimization differently.The first type, interference reduction, is used in conjunction withcoverage and capacity optimization. The interference reduction is doneby implementing RF techniques such as antenna tilt, transmit powerreduction, and handover mechanisms. The second type, ICIC, is usedexclusively for cell edge user equipment (UE), to which the samePhysical Resource Blocks (PRBs) have been assigned by the servingwireless cell as those assigned in other wireless cells to theirassociated UEs that cause the interference.

The LTE Recommendation has defined a new interface between base stationsto enable the transfer of ICIC function indicators. This interface isreferred to as X2. These function indicators are: Relative NarrowbandTransmit Power Indicator (“RNTPI”), High Interference Indicator (“HII”),and Interference Overload Indicator (“OI”).

The RNTPI indicator message is sent to neighbor base stations (referredto herein as “eNBs”). It contains one bit per each Physical ResourceBlock (PRB) in the downlink transmission, which indicates if thetransmission power associated with that PRB will be greater than apre-defined threshold. Thus, neighbor eNBs may anticipate which bandswould suffer more severe interference and take the appropriatescheduling decisions immediately, rather than wait to receive and relyon the UEs' Channel Quality Information (“CQI”) reports.

The HII indicator for uplink transmissions has a somewhat similarfunction as that which was described above in connection with the RNTPImessage for downlink transmissions. There is one bit per each PRB,enabling the neighboring eNBs to assess whether they should expect highinterference power in the near future. Typically, only PRBs that areassigned to cell-edge UEs are indicated by these messages. ReferenceSignal Received Power (“RSRP”) measurements which are reported as partof handover measurement reports, can identify cell edge UEs. In asimilar manner, this indicator can be used to identify the bands used ina frequency partitioning scheme.

While the previously described X2 messages are sent out proactively bythe eNBs, the overload indicator (“OI”) is only triggered whenhigh-interference in the uplink direction is detected by an eNB. In sucha case, an overload indication will be sent to neighbor eNBs whose UEsare potentially the source of this high interference. The messagecontains a low, medium or high interference level indication per eachPRB. However, the question, which cell is the one responsible for thehigh interference is of course not a trivial question to answer.

According to 3GPP TS 36300-970, Inter-cell interference coordination isassociated with managing radio resources (notably the radio resourceblocks) such that inter-cell interference is kept under control. ICIC isinherently a multi-cell, radio resource management (“RRM”) function thatneeds to take into account information (e.g. the resource usage statusand traffic load situation) obtained from various cells. Furthermore, anICIC method may be different in the uplink and downlink.

3GPP release 10 introduces a new LTE network concept which is defined asheterogeneous networks (“HetNet”), in contrast to previous networkreleases which deal with homogeneous networks. HetNet is defined as anetwork of eNBs with different capabilities, most importantly, differentTx-power classes.

However, heterogeneous networks pose new ICIC challenges. A first ICICchallenge involves Macro UE that roams about a Home eNB (HeNB) and isnot part of the closed subscriber group (“CSG”). In that scenario theMacro eNB UE transmission will become uplink interference to the HomeeNB authorized UEs. The second ICIC challenge is Macro eNB transmissionto cell edge UEs that forms downlink interference to Pico eNB centercell UE. In order to enable the use of HetNet, enhanced ICIC (eICIC)Rel. 10 requires that all members of a HetNet (Macro, Pico, HeNB) shouldbe capable of interconnecting by using the X2 interface.

Another major problem is that the ICIC is limited to data channels.Therefore, the recommendation does not provide sufficient protection forthe downlink control channels in the two above-mentioned severeinterference scenarios. Furthermore, range expansion has to be limitedto small offsets between cells, in order to keep control channel errorsat a reasonable level. Hence for Rel. 10 3GPP two new approaches wereproposed to avoid heavy inter-cell interference on both data and controlchannels in the downlink direction. One is based on carrier aggregationwith cross-carrier scheduling, while the other is based on time-domainmultiplexing (“TDM”) using so called almost blank sub-frames (“ABS”).

Carrier Aggregation is one of the most important features of the LTEAdvanced. Unlike LTE, it enables an LTE-A UE to connect to severalcarriers simultaneously. It not only allows resource allocation acrosscarriers, it also allows implementing a scheduler based on fastswitching between carriers without time consuming handover.

SUMMARY OF THE DISCLOSURE

The disclosure may be summarized by referring to the appended claims.

It is an object of the present invention to provide a method andapparatus to enable reducing interference in a wireless network.

It is another object of the present invention to provide a method and anapparatus to enable reducing interference in a wireless network byrelying on information that relates to the most interfered groups ofallocated radio resources.

It is still another object of the present invention to provide a methodand an apparatus to enable reducing interference in a wireless networkby forcing a change in the definitions of neighboring wireless cellsand/or in the definitions of the classifications of user equipmentwithin wireless cells.

Other objects of the present invention will become apparent from thefollowing description.

According to one embodiment, there is provided a method for reducinginter-cell interferences in a wireless communication network comprisinga plurality of wireless cells by invoking Inter-cell interferencecoordination (“ICIC”) procedure, the method comprises the steps of:

-   (a) identifying one or more of the plurality of wireless cells which    experience more interference than the remaining of the plurality of    wireless cells;-   (b) identifying at least one group of allocated radio resources    (e.g. Physical Resource Block (PRB)) for transmission to/from the    one or more identified wireless cells, and wherein transmissions    made while utilizing the at least one identified group of allocated    radio resources, are characterized as being subjected to more    interference than concurrent transmissions made while utilizing the    other groups of allocated radio resources for transmission to/from    the one or more identified wireless cells;-   (c) for each of the at least one identified group of allocated radio    resources, identifying two or more user equipments (UEs) utilizing    that group of allocated radio resources, and determining whether the    location of at least one of the UEs is at the edge of a wireless    cell at which the respective UE is provided with communication    services;-   (d) selecting one pair of UEs from among the two or more UEs,    wherein the current location of one member of that pair of UEs is at    an edge of a first wireless cell associated therewith and the    current location of the other member of the UEs pairs is either:    -   i) located at a second wireless cell which is currently not        included in a neighbors' list of the first wireless cell, or    -   ii) located at a second wireless cell which is adjacent to the        first wireless cell, as long as that other UE member is located        away from the second wireless cell's edge which is located        adjacent to an edge of the first wireless cell;

(d1) for a selected pair of UEs in which the other UE member is locatedat a second wireless cell currently not included of a neighbors' list ofthe first wireless cell (i.e. option (i)), including the second wirelesscell in the neighbors' list of the first wireless cell;

(d2) for a selected pair of UEs in which the other UE member is locatedat a second wireless cell adjacent to the first wireless cell but awayfrom the second wireless cell's edge which is adjacent to an edge of thefirst wireless cell (i.e. option (ii)), falsely defining that othermember as being a UE located at the second wireless cell's edge which isadjacent to an edge of the first wireless cell; and

(e) invoking an Inter-cell interference coordination procedure involvingthe selected pair of UEs, thereby reducing inter-cell interferences.

As will be appreciated by those skilled in the art, step (d1)/(d2) andstep (e) may then be repeated for other such selected pairs.

In the following description, the wireless communication network isdescribed in terms of a wireless network being in compliance with 3GPPLong Term Evolution (LTE) Recommendation. Nevertheless, it should beunderstood that the present invention is not restricted to this specificRecommendation (standard) but rather may be implemented in conjunctionwith any applicable standard, mutatis mutandis.

In LTE, both OFDMA (Orthogonal Frequency Division Multiple Access) andSC-FDMA (Single Carrier-Frequency Division Multiple Access) are defined.Both of them utilize 15 KHz subcarriers which are then grouped intoPhysical Resource Blocks (PRB), each containing 12 subcarriers whichamounts to 180 KHz of the spectrum. The present invention relates to agroup of allocated radio resources, which, as one of its options, whenrelating to the LTE Recommendation, is the equivalent of a PhysicalResource Block (PRB). Although the following description is provided interms of PRBs to ease on the reading, it should be understood that theinvention is not limited to the networks complied with LTErecommendation, nor to the use of PRBs, and encompasses all applicablecases where there is a use of a group of allocated radio resources asmeant herein.

According to another embodiment, step (a) of the method provided istriggered when the number of successful HARQ events associated with agiven wireless cell divided by the sum of HARQ events associated withthe given wireless cell (both successful and unsuccessful events) isless than the number of successful HARQ events divided by the sum ofHARQ events (both successful and unsuccessful events) for the wirelesscells included in a cluster of wireless cells to which the given cellbelongs, less a pre-defined factor being a function of the standarddeviation of the successful HARQ events divided by the sum of successfuland unsuccessful HARQ events associated with the wireless cellsbelonging to that cluster.

In accordance with another embodiment, step (c) comprises retrievinginformation which relates to Radio Resource Control (RRC) ConnectionSetup for a plurality of UEs and based on the information retrieved,determining the UEs located at the most interfered wireless cell and theUEs associated with the most interfered PRBs.

By yet another embodiment, the step of determining whether the locationof the one or more UEs is at the edge of its respective wireless cell,is based upon retrieving time adjustment (TA) and/or received signalstrength power (RSSP) values of the UEs whose identities wereestablished, and comparing each of the retrieved TA and RSSP values withpredetermined threshold values, so that if the TA value is greater thana first pre-defined threshold value and/or the RSSP value is less than asecond pre-defined value, the respective UE is determined to be locatedat the cell edge.

According to still another embodiment, step (d1) comprises utilizing therespective UE's RRC Connection Setup information in order to identifywireless cells that are not currently included in the neighbors' list ofthat wireless cell, but which comprise UEs that are associated with themost interfered PRB.

Step (d1) may further comprise comparing the TA and/or RSSP values ofeach UE connected to a wireless cell which is currently not included inthe wireless cell's neighbors' list, to predetermined threshold valuesand if the respective TA value is greater than a first pre-definedthreshold value, and/or the RSSP value is less than a second pre-definedvalue, determining that this UE is located at the cell edge of awireless cell that is currently not included in its neighbors' list(e.g. an adjacent non-neighboring wireless cell).

By yet another embodiment, step (d1) further comprises identifying fromamong the UEs determined to be located at an edge of a respectivewireless cell which is not currently included in the wireless cell'sneighbors list, which one or more UEs are associated with the mostinterfered PRB(s).

According to another embodiment, step (e) comprises invoking anInter-cell interference coordination (ICIC) procedure between the firstand second wireless cells that are defined as being neighboring cellseven though that the second wireless cell was not included in theneighbors' list of the first wireless cell prior to carrying out step(d1).

According to still another embodiment, step (e) comprises invoking anInter-cell interference coordination (ICIC) procedure between the firstand second wireless cells even though one of the interfering/interferedUEs is currently located at the core of its wireless cell.

In accordance with another embodiment, the method provided furthercomprising a step of monitoring high interference indicator (HII)messages sent from a plurality of wireless cells, wherein each of theHII messages comprises a list of PRBs that are scheduled for a cell edgeUEs, and storing the PRBs together with the identities of theirassociated wireless cell and a timestamp indicating the time at whichthe HII message was sent.

Preferably, in step (d1) one or more wireless cells are identified asnot being included in the neighbors' list of the first wireless cell,and wherein the identification is carried based on information thatrelates to the stored PRBs, the identities of their associated wirelesscells and their respective timestamp.

In accordance with another embodiment, if by following step (c) it isdetermined that the one or more identified most interfered PRBs are notassociated with UEs located at a cell edge, determining the identitiesof the UEs that are connected to the most interfered base station whichare associated with the most interfered PRBs.

The values of the TA and the received signal strength power (RSSP) ofeach UE connected to an adjacent neighboring base station, are comparedwith predetermined threshold values and if the respective TA value isless than the first threshold value and the received signal strengthpower (RSSP) value is higher than the second value, determining thatthat UE is located at the cell core of the adjacent neighboring wirelesscell thereof.

By yet another embodiment, the method further comprising a step ofidentifying the adjacent neighboring wireless cells that compriseidentifications of cell core UEs connected thereto and associated withthe one or more of the most interfered PRB(s).

In accordance with still another embodiment, the method provided furthercomprising a step of conveying an HII message to all of the identifiedadjacent neighboring wireless cells, wherein the most interfered PRBwhich was found to be associated with a cell core UE, will be falselyidentified for the adjacent neighboring wireless cells as being a celledge PRB, in order to enable invoking an Inter-cell interferencecoordination (ICIC) procedure, thereby reducing inter-cellinterferences.

In accordance with still another embodiment, the method provided furthercomprises a step of changing the cell edge to cell core ratio of thewireless cell, wherein the most interfered PRB which was found to beassociated with a cell core UE, will now be associated with a cell edgeUE and will be categorized as cell edge PRB in order to enable invokingan Inter-cell interference coordination (ICIC) procedure, therebyreducing inter-cell interferences. In other words, in the case it is notpossible to tag a UE as a cell core and if there exists a base stationparameter that defines a ratio between cell edge and cell core, than bychanging that parameter one is able to effectively force cell core UEsto be regarded as cell edge UEs without the need to send an artificialHII message.

In accordance with still another embodiment, the method provided furthercomprising a step of changing the tilt of the antenna associated withthe wireless cell so that interference energy due to transmissionsfrom/to other wireless cells is minimized.

According to another aspect, there is provided a controller adapted toreduce inter-cell interferences in a wireless communication networkcomprising a plurality of wireless cells, the controller is adapted tocarry out the following operations:

-   (a) identify one or more of the plurality of wireless cells which    experience more interference than the remaining of the plurality of    wireless cells;-   (b) identify at least one group of allocated radio resources    transmitted to/from the one or more identified wireless cells, and    wherein transmissions made while utilizing the at least one    identified group of allocated radio resources, are characterized as    being subjected to more interference than concurrent transmissions    made while utilizing the other groups of allocated radio resources    for transmission to/from the one or more identified wireless cells;-   (c) for each of the at least one identified group of allocated radio    resources, identify two or more user equipments (UEs) utilizing that    group of allocated radio resources, and determine whether the    location of at least one of these UEs is at the edge of a wireless    cell at which the respective UE is provided with communication    services;-   (d) select one pair of UEs from among the two or more UEs, wherein    the current location of one member of that pair of UEs is at an edge    of a first wireless cell associated therewith and the current    location of the other member of the UEs pairs is either:    -   i) located at a second wireless cell which is currently not        included in a neighbors' list of the first wireless cell, or    -   ii) located at a second wireless cell which is adjacent to the        first wireless cell, as long as that other UE member is located        away from the second wireless cell's edge which is located        adjacent to an edge of the first wireless cell;

(d1) for a selected pair of UEs in which the other UE member is locatedat a second wireless cell currently not included of a neighbors' list ofthe first wireless cell, include the second wireless cell in theneighbors' list of the first wireless cell;

(d2) for a selected pair of UEs in which the other UE member is locatedat a second wireless cell adjacent to the first wireless cell but awayfrom the second wireless cell's edge which is adjacent to an edge of thefirst wireless cell, falsely define that other member as being a UElocated at the second wireless cell's edge which is adjacent to an edgeof the first wireless cell; and

(e) invoke an Inter-cell interference coordination procedure involvingthe selected pair of UEs, thereby reducing inter-cell interferences.

Other aspects of the present invention such as certain features of thecontroller and a communication system, which are adapted to operate inaccordance with the principles of the method described hereinabove,mutatis mutandis, are encompassed within the scope of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following detailed description taken in conjunction withthe accompanying drawings wherein:

FIG. 1—is a schematic illustration of a schematic block diagram of anintegrated cICIC controller;

FIG. 2—demonstrates a schematic illustration of a configuration in whicha missing neighbor interference type is possible;

FIG. 3—exemplifies an embodiment of a method for carrying out missingneighbor interference mitigation without X2 signaling monitoring;

FIG. 4—exemplifies an embodiment of a method for carrying out missingneighbor interference mitigation with X2 signaling monitoring;

FIG. 5—demonstrates a schematic illustration of a configuration of awrong PRB mapping interference;

FIG. 6—exemplifies an embodiment of a method for carrying out a wrongPRB mapping interference mitigation without X2 signaling monitoring; and

FIG. 7—exemplifies an embodiment of a method for carrying out a wrongPRB mapping interference mitigation with X2 signaling monitoring.

DETAILED DESCRIPTION

In this disclosure, the term “comprising” is intended to have anopen-ended meaning so that when a first element is stated as comprisinga second element, the first element may also include one or more otherelements that are not necessarily identified or described herein, orrecited in the claims.

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a betterunderstanding of the present invention by way of examples. It should beapparent, however, that the present invention may be practiced withoutthese specific details.

Let us first consider FIG. 1, which illustrates a schematic example of ablock diagram of an integrated cICIC controller. The centralized ICIC(referred to herein as “cICIC”) controller is connected in this exampleto the network's Operation Support System (“OSS”) via an It-FN businterface, and sends, among many other messages, add/delete neighborcommands or HII messages or new threshold values to the appropriate basestation cells via an IP bus.

The cICIC controller obtains from the OSS the mapping of all basestation cells, their identification codes as well as their IP addressesand their associated neighbors' lists. In addition, the cICIC controllerobtains from the OSS the number of hybrid automatic repeat request(“HARQ”) success events and the number of HARQ unsuccessful (failed)events on a per wireless cell basis, i.e. the number of successful andunsuccessful combinations of high-rate forward error-correcting codingand ARQ error-control in each of a plurality of wireless cells (e.g. FDDcells). The number of HARQ events typically depends on the radioenvironment (higher noise level implies greater number of HARQ events)and on the user throughput requirements (less data entails less HARQevents). In order to eliminate the data throughput dependency, a successrate criteria which is defined as follows, may be used:

HARQ Success rate=HARQ success events/(HARQ success events+HARQ failevents)

The cICIC controller maps the deployed base stations into clusters (oralternatively the wireless cells at which the base stations aredeployed), wherein each cluster includes at least one base stationassociated with at least one wireless cell. The cICIC controller thancalculates, preferably on ongoing basis, the average HARQ success rateand the standard deviation of the HARQ success rate. If the HARQ successrate associated with a specific wireless cell is found to be less thanthe cluster's average HARQ success rate for the wireless cells includedin that cluster less a factor which is a function of the standarddeviation, an indication is triggered to alert the operator of thissituation.

A large number of unsuccessful HARQ events (when compared with thenumber of successful HARQ events) are attributed to excessiveinterference. The interference may be classified into two types ofinterferences. The first, interference experienced by cell edge userequipments, UEs, caused by wireless cells which are not part of theneighbors' list, (e.g. by neighbors not included in the neighbors' list,by non-geographically adjacent wireless cells, etc.) in which the samePRBs are used. The second, interference to cell core user equipmentscaused by neighboring wireless cells which use the same PRBs whilecommunicating with their cell core UEs.

For the convenience of the reader, reference will be made hereinafter tothe first interference type as “Missing Neighbor interference”, and thesecond interference type will be referred to as “Wrong PRB Mappinginterference”.

FIG. 2 illustrates a configuration in which missing neighborinterference type mitigation is possible. In this missing neighborinterference scenario, cell 1C comprises a UE located at cell edge andto which PRB1 has been allocated. Cell 3B, which is not geographicallyadjacent to cell 1C and is not included in the neighbors' list ofwireless cell 1C, also comprises a UE at its cell edge using PRB1. It isassumed for the sake of this example that the network radio conditionsare such, that the UE in cell 1C does not consider cell 3B to be a validcell for receiving radio services therefrom. Similarly the UE in cell 3Bdoes not consider cell 1C to be a valid option for receiving services.Due to the fact that cells 1C and 3B are not geographical neighbors, thebase station ICIC mechanism as known in the prior art is not activated,and consequently the RF transmission by/to the UE in cell 3B createsinterference to the UE of cell 1C.

According to the solution provided herein for overcoming the missingneighbor interference problem, the potential missing neighbors areidentified, they are then defined as neighbors of the given cell (eventhough, as explained above, they are not included in the neighbors' listof the given cell, e.g. not being geographical neighbors thereof), andthen the ICIC mechanism of the base station of the given cell is used tocoordinate and mitigate the missing neighbor interference.

Following are two possible implementations of this solution. The firstone (exemplified in FIG. 3) does not involve using X2 signalingmonitoring (i.e. X2 signaling over the IP bus) and the second one(exemplified in FIG. 4) involves using X2 signaling monitoring.

FIG. 3 exemplifies an embodiment of a method encompassed by the presentinvention for carrying out missing neighbor interference mitigationwithout X2 signaling monitoring, which comprises the following steps:

Once a HARQ indication is triggered (step 300) (i.e. when the HARQsuccess rate associated with a given wireless cell is less than theaverage HARQ success rate for the wireless cells included in thatcluster to which the given cell belongs, less a factor which is afunction of the standard deviation), the cICIC controller identifies(step 305) the one (or more) most interfered wireless cell(s) (e.g. theeNB cell subjected to the larger interferences), the cluster with whichit is associated, and the timestamp of the respective HARQ success rate.

The cICIC controller then identifies the PRB noise measurements for eachmost interfered base station (i.e. the base station (e.g. eNB) of themost interfered wireless cells) (step 310), and from data received alongits It-FN bus, the cICIC controller is able to determine (step 315) one(or more) most interfered PRB associated with the most interfered basestation(s) (i.e. PRB for sending/receiving communications by the mostinterfered base station(s)).

The available Radio Resource Control (RRC) Connection Setup informationis examined (e.g. by the cICIC controller based on information receivedalong its It-FN bus) in order to determine which are the UEs that are incommunication with the most interfered base station, and which UEs areassociated with the most interfered PRBs (step 320).

Next, it is determined whether the most interfered PRB is associatedwith a cell edge UE (step 325), and based on the available RRCConnection Setup information (e.g. retrieved along the cICIC controllerIt-FN bus), the identities of the UEs that are connected to the mostinterfered wireless cell which are also associated with the mostinterfered PRB(s), are established (step 330).

The time adjustment (TA) value and the received signal strength power(RSSP) (e.g. retrieved from the It-FN bus) of the UEs whose identitieswere established in step 330, provide an indication for the estimateddistance extending between the UE and its serving base station (step335). The TA and RSSP values are compared with predetermined thresholdvalues and if the respective TA value is larger than a first thresholdvalue and the received signal strength power (RSSP) value is less thanthe second value, the respective UE is determined to be located at acell edge (step 340).

The cICIC controller maintains a list of base stations that are locatedat the vicinity of every base station (but not included in its list ofneighboring base stations), and a list of neighbors for every basestation. The cICIC controller examines the UEs' RRC Connection Setupinformation in order to identify adjacent, yet non-neighboring wirelesscells comprising UEs that are associated with the most interfered PRB(s)(step 345).

Then, the cICIC controller determines whether a most interfered PRB isassociated with a cell edge UE connected to an adjacent, non-neighboringbase station (step 350), by comparing the TA and RSSP values of each UEconnected to an adjacent, non-neighboring base station to predeterminedthreshold values and if the TA value is found to be higher than thefirst threshold value and/or the RSSP value is found to be less than thesecond threshold value, the cICIC controller concludes that the UE ofthe non-neighboring wireless cell is located at a cell edge.

Thereafter, the cICIC controller compiles a list of adjacent butnon-neighboring base stations, which serve the cell edge UEs that areassociated with the most interfered PRB(s) (step 355).

Then cICIC controller sends an “add neighbor” command to all of the basestations in the above compiled list (preferably over the IP bus), andfollowing the receipt of this command, the respective base stations thatare included in that list, change the status of the most interfered basestation (step 360) to a new status, by defining that most interferedbase station to be their neighbor. In other words, the cICIC controllerinitiates a forced neighboring relationship between base stations ofwireless cells that are not part of the neighbors' list of the mostinterfered wireless cell, e.g. they are not geographical neighbors tothe most interfered wireless cell, and the base station of the mostinterfered wireless cell.

Following a predetermined timeout, the cICIC controller reexamines thenew value of the HARQ success rate of the most interfered base stationin order to determine whether the above procedure has been successful(step 365) (e.g. is the wireless cell that was previously identified ashaving the most interfered base station, has no longer the mostinterfered base station). If the above procedure is not found to besuccessful, the process is reversed by issuing a “delete neighbor”command, thereby removing all the adjacent, non-neighboring basestations from the neighbors' list of the base station that was the mostinterfered base station (step 370), and of the respective base stationsthat were defined by the cICIC controller as its neighbors. Steps 305 to370 are repeated, triggering a new HARQ indication in accordance withstep 300.

FIG. 4 exemplifies an embodiment of a method for carrying out a missingneighbor interference mitigation with X2 signaling monitoring. Accordingto this embodiment, the cICIC controller monitors the base stations' HIImessages sent over the IP bus (step 400), where each HII messagecomprises a list of PRBs that are scheduled to be associated with celledge UEs. The PRBs are stored and a record thereof is maintainedtogether with its respective base station (or alternatively itsrespective wireless cell) identity and a timestamp indicating the timeat which the HIT message was sent.

Once a HARQ indication is triggered as discussed in the previous example(step 300), the cICIC controller identifies the most interfered wirelesscell (or alternatively the most interfered base station), the cluster itis associated with, and the timestamp of the respective HARQ events.

The cICIC controller then identifies the PRB noise measurements for eachof the most interfered base stations (step 405), and from data receivedalong its It-FN bus, it is able to determine the one (or more) mostinterfered PRB associated with the most interfered base station(s) (step410).

The cICIC controller maintains a list of the base stations located atthe vicinity of every base station (but not being its geographicalneighbor) as well as a list of the adjacent neighbors, for every basestation. It then examines the stored records in order to compile a listof the base stations which are the most probable candidates to causeinterference based on time proximity between the recorded timestamps oftheir associated PRBs and the timestamp of the most interfered PRB (step415). The cICIC controller then compiles a list of adjacent,non-neighboring base stations (step 420) that are associated with themost interfered PRB.

Thereafter, The cICIC controller sends an “add neighbor” command to allbase stations included in the above compiled list (preferably over theIP bus) (step 425), and in response to that command, the definition ofall these base stations is forcedly changed to become the neighbors ofthe most interfered base station, and vice versa (step 430).

Following a predetermined timeout, the cICIC controller reexamines thevalue of the HARQ success rate of the most interfered base station inorder to determine whether the above procedure has been successful (step435) (e.g. is the base station that was identified as the mostinterfered base station, no longer the most interfered base station),and if not, (step 440) the process is reversed by issuing a “deleteneighbor” command, thereby removing all the adjacent, non-neighboringbase stations from the neighbors' list of the base station that was themost interfered one, and vice versa. Upon receiving a new HARQindication, repeating steps 405 to 440).

FIG. 5 illustrates a configuration of a wrong PRB mapping, in which cell1C comprises a UE located at cell center to which PRB1 has beenallocated, and Cell 2A, which is geographically adjacent to cell 1C (aneighbor of C1), also comprises a UE at its cell edge using PRB1. Due tothe fact that cells 10 and 2A are neighbors of each other and therespective UEs are at cell center, the ICIC mechanism is not activatedand the RF transmission by the UE in cell 2A creates UL interference atcell 1C (and vise versa).

According to the solution provided herein for overcoming the wrong PRBmapping interference problem, the potentially interfering cell core PRBsare identified, they are then defined as cell edge PRBs, and then theICIC mechanism of the base station of the given cell is used tocoordinate and mitigate the wrong PRB mapping interference.

Following are two possible implementations of the present solution toovercome this problem. The first one does not involve using X2 signalingmonitoring (i.e. X2 signaling over the IP bus) while the second oneinvolves using X2 signaling monitoring.

FIG. 6 exemplifies an embodiment of a method for carrying out a wrongPRB mapping interference mitigation without X2 signaling monitoring. Themethod according to this embodiment comprises the following steps:

Once a HARQ indication is triggered as discussed above (step 300), thecICIC controller identifies (step 600) the most interfered wireless cell(or rather the base station associated therewith), the cluster it isassociated with, and the timestamp of the respective HARQ success rate.

The cICIC controller uses the PRB noise measurements of the base stationin the most interfered wireless cell (e.g. data received along its It-FNbus), to determine the most interfered PRB associated with the mostinterfered wireless cell (step 605).

The cICIC controller examines (step 610) the available Radio ResourceControl (RRC) Connection Setup information (e.g. information receivedalong its It-FN bus) in order to determine which are the UEs that areassociated (e.g. connected) with the most interfered wireless cell, andwhich UEs are associated with the most interfered PRBs.

Next, it determines whether the most interfered PRB is associated with acell core UE (step 615), and based on the available RRC Connection Setupinformation (e.g. retrieved via the cICIC controller's It-FN bus),establishes the identities of the UEs that are connected to the mostinterfered base station and which are associated with the mostinterfered PRB(s) (step 620).

The time adjustment (TA) and the received signal strength power (RSSP)values (e.g. retrieved from the It-FN bus) of the UEs whose identitieswere established, are then applied in order to enable estimating thedistance extending between the UE and its respective serving basestation. The TA and RSSP values are compared with predeterminedthreshold values, and if the TA value is found to be less than a firstthreshold value and/or the RSSP value is found to be over a secondthreshold value, the respective UE is determined to be located at a cellcore (step 625).

The cICIC controller maintains a list of base stations that are locatedat the vicinity (but not a neighbor) of every base station and a list ofthe associated neighbors, for every base station. It then examines theUEs' RRC Connection Setup information in order to identify adjacentneighboring wireless cells comprising UEs that are associated with themost interfered PRB (step 630).

Then, the cICIC controller determines whether the most interfered PRB isassociated with a cell core UE connected to a base station located in anadjacent neighboring wireless cell (step 635). The cICIC controllercompares the TA and RSSP values of each UE connected to an adjacentneighboring base station, with predetermined threshold values and if theTA value is found to be less than that first threshold value and/or theRSSP value is found to be higher than the second threshold value, thecICIC controller concludes that this UE is located at a cell core of theneighboring wireless cell.

Thereafter, the cICIC controller compiles a list of adjacent neighboringbase stations that comprises identifications of cell core UEs connectedto these base stations which are associated with the most interferedPRB(s) (step 640), and sends (step 645) an X2 HII message to all thebase stations included in the list compiled in step 640 (preferably overthe IP bus), in which the most interfered PRB, even though it was foundto be associated with a cell core UE, would be falsely identified forthe base stations as being a cell edge PRB, in order to enable invokingthe ICIC mechanism (step 645).

Following a predetermined timeout, the cICIC controller reexamines thevalue of the HARQ success rate of the most interfered base station inorder to determine whether the above procedure has been successful (step650) (e.g. is the wireless cell that was identified as the mostinterfered wireless cell, no longer the most interfered wireless cell).If the most interfered wireless cell is still found to be the mostinterfered eNB cell, an error message will be issued (step 655). Steps600 to 655 are repeated when a new HARQ indication is triggered.

FIG. 7 exemplifies an embodiment of a method for carrying out a wrongPRB mapping interference mitigation with X2 signaling monitoring, whichcomprises the following steps.

The cICIC controller monitors eNB cell HII messages sent over the IP bus(step 700). Each HII message comprises a list of PRBs that are scheduledto be assigned to cell core UEs. The PRBs are stored and a recordthereof is maintained (step 705) together with the eNB cell identity anda timestamp indicating the time at which the HII message was sent.

Once a HARQ indication is triggered as discussed above (see step 300 ofFIG. 3), the cICIC controller identifies the most interfered eNB cell,the cluster it is associated with, and the timestamp of the respectiveHARQ events (step 710).

The cICIC controller then identifies the PRB noise measurements for eachof the most interfered eNB cells from data received along its It-FN bus(step 715), and determines (step 720) the one (or more) most interferedPRB associated with the most interfered eNB cell(s).

The cICIC controller maintains a list of the eNB cells that are at thevicinity of every eNB cell, and a list of the associated neighbors forevery eNB cell. It examines the stored records in order to compile alist of the eNB cells which are the most probable candidates to causeinterference, based on the proximity between the recorded timestamps oftheir associated PRB that do not comprise the most interfered PRB (step725). The underlying assumption here is that if the most interfered PRBis not associated with cell edge UEs, it is most probably associatedwith cell core UEs. The cICIC controller compiles a list of neighbor eNBcells that most probably have assigned the most interfered PRB to cellcore UEs (step 730) and compiles a list of neighboring eNB cells thatare most likely associated with the most interfered PRB to cell core UEs(step 735).

The cICIC controller sends (step 740) an X2 HII message to all of theeNB cells in the above compiled list (preferably over the IP bus), inwhich the most interfered PRB even though it is associated with a cellcore UE, would be falsely identified for the eNB cells as being a celledge PRB, in order to enable invoking the ICIC mechanism (step 745).

Following a predetermined timeout, the cICIC controller reexamines thevalue of the HARQ success rate of the most interfered eNB cell in orderto determine whether the above procedure has been successfully conducted(step 747) (e.g. is the eNB cell that was identified as the mostinterfered eNB cell, is no longer the most interfered eNB cell), but ifthe most interfered eNB cell still remains the most interfered eNB cell,an error message will be issued (step 750). Steps 700 to 750 arerepeated every time a new HARQ indication is triggered.

The present invention has been described using detailed descriptions ofembodiments thereof that are provided by way of example and are notintended to limit the scope of the invention in any way. The describedembodiments comprise different features, not all of which are requiredin all embodiments of the invention. Some embodiments of the presentinvention utilize only some of the features or possible combinations ofthe features. Variations of embodiments of the present invention thatare described and embodiments of the present invention comprisingdifferent combinations of features noted in the described embodimentswill occur to persons of the art. For example, determining whichwireless cell is the most interfered cell can be done on a PRB basis oron any other applicable time basis which will is applicable to thevarious wireless cells. The scope of the invention is limited only bythe following claims.

1. A method for reducing interferences in a wireless communicationnetwork comprising a plurality of wireless cells, the method comprisesthe steps of: (a) identifying one or more of the plurality of wirelesscells which experience more interference than the remaining of theplurality of wireless cells; (b) identifying at least one group ofallocated radio resources for transmission to/from the one or moreidentified wireless cells, and wherein transmissions made whileutilizing the at least one identified group of allocated radioresources, are characterized as being subjected to more interferencethan concurrent transmissions made while utilizing the other groups ofallocated radio resources for transmission to/from the one or moreidentified wireless cells; (c) for each of the at least one identifiedgroup of allocated radio resources, identifying two or more userequipments (UEs) utilizing that group of allocated radio resources, anddetermining whether the location of at least one of the UEs is at theedge of a wireless cell at which the respective UE is provided withcommunication services; (d) selecting one pair of UEs from among the twoor more UEs, wherein the current location of one member of that pair ofUEs is at an edge of a first wireless cell associated therewith and thecurrent location of the other member of the UEs pairs is either: i)located at a second wireless cell which is currently not included in aneighbors' list of the first wireless cell, or ii) located at a secondwireless cell which is adjacent to the first wireless cell, as long asthat other UE member is located away from the second wireless cell'sedge which is located adjacent to an edge of the first wireless cell;(d1) for a selected pair of UEs in which the other UE member is locatedat a second wireless cell currently not included of a neighbors' list ofthe first wireless cell, including the second wireless cell in theneighbors' list of the first wireless cell; (d2) for a selected pair ofUEs in which the other UE member is located at a second wireless celladjacent to the first wireless cell but away from the second wirelesscell's edge which is adjacent to an edge of the first wireless cell,falsely defining said other member as being a UE located at the secondwireless cell's edge which is adjacent to an edge of the first wirelesscell; and (e) invoking an Inter-cell interference coordination procedureinvolving the selected pair of UEs, thereby reducing inter-cellinterferences.
 2. The method of claim 1, wherein step (a) is triggeredwhen the number of successful HARQ events associated with a givenwireless cell divided by the sum of HARQ events associated with saidgiven wireless cell is less than the average HARQ success rate for thewireless cells included in a cluster of wireless cells to which thegiven cell belongs, minus a pre-defined factor being a function of astandard deviation of successful HARQ events divided by the sum of HARQevents associated with the wireless cells of said cluster.
 3. The methodof claim 1, wherein step (c) comprises retrieving information whichrelates to Radio Resource Control (RRC) Connection Setup for a pluralityof UEs and based on the information retrieved, determining the UEsconnected to the most interfered base station and the UEs associatedwith the most interfered group of allocated radio resources.
 4. Themethod of claim 1, wherein the step of determining whether the locationof the one or more UEs is at the edge of its respective wireless cell,is based upon retrieving time adjustment (TA) value and/or receivedsignal strength power (RSSP) value for the UEs whose identities wereestablished, and comparing each of the retrieved TA and/or RSSP valueswith respective predetermined threshold values, so that if said TA valueis greater than a first threshold value and/or said RSSP value is lessthan a second threshold value, the respective UE is determined to belocated at the cell edge.
 5. The method of claim 1, wherein step (d1)comprises utilizing RRC Connection Setup information of a respectiveUE's in order to identify wireless cells that are not currently includedin said neighbors' list, which comprise UEs that are associated with themost interfered group of allocated radio resources.
 6. The method ofclaim 5, wherein step (d1) further comprises comparing TA and RSSPvalues associated with each UE connected to a wireless cell which is notcurrently included in the wireless cell's neighbors list, topredetermined threshold values and if the respective TA value is greaterthan a first threshold value and/or the respective RSSP value is lessthan a second threshold value, determining that said UE is located atthe cell edge of a wireless cell which is not currently included in saidwireless cell's neighbors list.
 7. The method of claim 6, wherein step(d1) further comprises identifying from among the UEs determined to belocated at an edge of a respective wireless cell which is not currentlyincluded in said wireless cell's neighbors list, which one or more UEsare associated with the most interfered group(s) of allocated radioresources.
 8. The method of claim 1, wherein step (e) comprises invokingan Inter-cell interference coordination (ICIC) procedure between thefirst and second wireless cells that are defined as being neighboringcells even though the second wireless cell has not been included in theneighbors' list of the first wireless cell prior to carrying out step(d1).
 9. The method of claim 1, wherein step (e) comprises invoking anInter-cell interference coordination (ICIC) procedure between the firstand second wireless cells even though one of the interfering/interferedUEs is currently located at the core of its wireless cell.
 10. Themethod of claim 1, further comprising a step of monitoring highinterference indicator messages sent by a plurality of wireless cells,wherein each of said high interference indicator messages comprises alist of groups of radio resources' allocations that are scheduled for acell edge UEs, and storing said groups of radio resources' allocationstogether with the identity of their associated wireless cell and atimestamp indicating the time at which the high interference indicatormessage was sent.
 11. The method of claim 10, wherein step (d2) iscarried out based on information that relates to stored informationregarding groups of allocated radio resources, the identity of theirassociated wireless cell and their respective timestamp.
 12. The methodof claim 1, wherein if by following step (c) it is determined that theone or more identified most interfered groups of allocated radioresources are not associated with UEs located at a cell edge,determining identity of the UEs that are connected to the mostinterfered wireless cell and which are associated with the mostinterfered group of allocated radio resources.
 13. The method of claim12, further comprising a step of comparing TA and/or RSSP valuesassociated with each UE connected to an adjacent neighboring wirelesscell, to predetermined threshold values and if the respective TA valueis found to be less than a first threshold value and/or the respectiveRSSP value is found to be greater than a second threshold value,determining that said UE is located at the cell core of its adjacentneighboring wireless cell.
 14. The method of claim 13, furthercomprising a step of identifying the adjacent neighboring wireless cellsthat comprises identifications of cell core UEs connected thereto andassociated with the one or more of the most interfered groups ofallocated radio resources.
 15. The method of claim 14, furthercomprising a step of conveying an high interference indicator message toall of the identified adjacent neighboring wireless cells, wherein themost interfered group of allocated radio resources which was found to beassociated with a cell core UE, will be falsely identified for theadjacent neighboring wireless cells as being a group of allocated radioresources associated with a cell edge, in order to enable invoking aninter-cell interference coordination procedure, thereby reducinginter-cell interferences.
 16. The method of claim 1, further comprisinga step of inducing a change in a tilt of an antenna associated with saidwireless cell.
 17. A controller adapted to reduce interferences in awireless communication network comprising a plurality of wireless cells,the controller is adapted to carry out the following operations: (a)identify one or more of the plurality of wireless cells which experiencemore interference than the remaining of the plurality of wireless cells;(b) identify at least one group of allocated radio resources transmittedto/from the one or more identified wireless cells, and whereintransmissions made while utilizing the at least one identified group ofallocated radio resources, are characterized as being subjected to moreinterference than concurrent transmissions made while utilizing theother groups of allocated radio resources for transmission to/from theone or more identified wireless cells; (c) for each of the at least oneidentified group of allocated radio resources, identify two or more userequipments (UEs) utilizing that group of allocated radio resources, anddetermine whether the location of at least one of these UEs is at theedge of a wireless cell at which the respective UE is provided withcommunication services; (d) select one pair of UEs from among the two ormore UEs, wherein the current location of one member of that pair of UEsis at an edge of a first wireless cell associated therewith and thecurrent location of the other member of the UEs pairs is either: i)located at a second wireless cell which is currently not included in aneighbors' list of the first wireless cell, or ii) located at a secondwireless cell which is adjacent to the first wireless cell, as long asthat other UE member is located away from the second wireless cell'sedge which is located adjacent to an edge of the first wireless cell;(d1) for a selected pair of UEs in which the other UE member is locatedat a second wireless cell currently not included of a neighbors' list ofthe first wireless cell, include the second wireless cell in theneighbors' list of the first wireless cell; (d2) for a selected pair ofUEs in which the other UE member is located at a second wireless celladjacent to the first wireless cell but away from the second wirelesscell's edge which is adjacent to an edge of the first wireless cell,falsely define that other member as being a UE located at the secondwireless cell's edge which is adjacent to an edge of the first wirelesscell; and (e) invoke an Inter-cell interference coordination procedureinvolving the selected pair of UEs, thereby reducing inter-cellinterferences.